<div class="list-group">
   <a href="<%= admin_users_path %>" class="<%= href_active?("users") %>">用户管理</a> 
   <a href="<%= admin_articles_path %>" class="<%= href_active?("articles") %>">文章管理</a>
   <a href="<%= admin_categories_path %>" class="<%= href_active?("categories") %>">分类管理</a>
</div>
